Sulfur dioxide recovery from stack gases
employing oxidation inhibitor

ABSTRACT

AN IMPROVED PROCESS FOR SCRUBBING POWER PLANT STACK GAS WITH LIME OF LIMESTONE SLURRIES TO REMOVE SULFUR OXIDES WHICH CONSISTS OF FEEDING LIME OR LIMESTONE ALONG WITH RECYCLE LIQUOR AND MAKEUP WATER TO A DELAY TANK; CIRCULATING THE SLURRY FORMED THROUGH A GAS SCRUBBER TO REMOVE SULFUR DIOXIDE FROM STACK GAS; ADVANCING SLURRY EQUIVALENT TO THAT MADE IN THE ABOVE DELAY WITH TANK COUNTERCURRENT TO THE GAS AND USING IT IN ANOTHER SCRUBBING STAGE OR STAGES; REMOVING A SIMILAR AMOUNT OF SLURRY FROM THIS SCRUBBING STAGE AND SEPARATING SOLIDS AND CALCINING THEM TO PRODUCE USABLE SULFUR DIOXIDE; RETURNING SEPARATED LIQUOR TO SCRUBBING CIRCUIT; AND REUSING CALCINED SOLIDS IN SCRUBBING CIRCUIT FOR REMOVAL OF SULFUR DIOXIDE; OXIDATION INHIBITOR IS ADDED TO KEEP THE SULFUR IN EASILY REGENERABLE CALCIUM SULFITE FORM. THE CALCIUM SULFITE IS HEATED TO DRIVE OFF SULFUR DIOXIDE FOR SULFURIC ACID MANUFACTURE AND SIMULTANEOUSLY REGENERATE LIME FOR REUSE IN SCRUBBING STACK GAS. UNWANTED CALCIUM SULFATE UNAVOIDABLY FORMED IS COARSER THAN CALCIUM SULFUITE OR REGENERATED LIME AND IS SEPARATED BY SIZE CLASSIFICATION AND DISCARDED. FLY ASH, IF PRESENT, CAN BE REMOVED AHEAD OF THE SULFUR DIOXIDE SCRUBBERS BY WET SCRUBBERS OR ELECTROSTATIC PRECIPITATORS.

DEFENSW'E PULlCATlON UNITED STATES PATENT OFFICE Published at therequest of the applicant or owner in accordance with the Notice of Dec.16, 1969, 869 O.G. 687. The abstracts 01 Defensive Publicationapplications are identified by distinctly numbered series and arearranged chronologically. The heading of each abstract indicates thenumber of pages of specification, including claims and sheets ofdrawings contained in the application as originally filed. The files ofthese applications are available to the public for inspection andreproduction may be purchased for 30 cents a sheet.

Defensive Publication applications have not been examined as to themerits of alleged invention. The Patent Olfice makes no assertion as tothe novelty of the disclosed subject matter.

PUBLISHED SEPTEMBER 21, 1971 SULFUR DIOXIDE RECOVERY FROM STACK GASESEMPLOYlN-G OXIDATION INHIBITOR Archie V. Slack, Wilson Lake Shores,Shelfield, Ala.

35660, and John M. Potts, 1010 Linwood Ave.,

Florence, Ala. 35630 Filed Oct. 7, 1970, Ser. No. 78,662 Int. Cl. Btlld47/00, 47/02 US. Cl. 23-2SQ 2 Sheets Drawing. 16 Pages Specification Animproved process for scrubbing power plant stack gas with lime orlimestone slurries to remove sulfur oxides which consists of feedinglime or limestone along with recycle liquor and makeup Water to a delaytank; circulating the slurry formed through a gas scrubber to removesulfur dioxide from stack gas; advancing slurry equivalent to that madein the above delay tank countercurrent to the gas and using it inanother scrubbing stage or stages; removing a similar amount of slurryfrom this scrubbing stage and separating solids and calcining them toproduce usable sulfur dioxide; returning separated liquor to scrubbingcircuit; and reusing calcined solids in scrubbing circuit for removal ofsulfur dioxide. Oxidation inhibitor is added to keep the sulfur ineasily regenerable calcium sulfite form. The calcium sulfite is heatedto drive oif sulfur dioxide for sulfuric acid manufacture andsimultaneously regenerate lime for reuse in scrubbing stack gas.Unwanted calcium sulfate unavoidably formed is coarser than calciumsulfite or regenerated lime and is separated by size classification anddiscarded. Fly ash, if present, can be removed ahead of the sulfurdioxide scrubbers by wet scrubbers or electrostatic precipitators,

REGENERATION,

Filed Oct.

A. V. SLACK ET AL SULFUR DIOXIDE RECOVERY FROM STACK GASES EMPLOYINGOXIDATION INHIBITOR 7, 1970 2 Sheets-Sheet 2 EFFECT OF TTME ANDTEMPERATURE ON REGENERTTON OF C080

